1. Field of the Invention
The present invention relates to a method for lubricating a dynamic pressure bearing.
2. Description of the Related Arts
Conventionally, a bearing for rotating accurately at high speed has employed a dynamic pressure bearing 100 as shown in a partial sectional view of FIG. 4. The shaft (rotation shaft) 101 is rotatably received in a sleeve 102. The sleeve 102 is fixed with a thrust plate 103 at a lower end. A dynamic pressure groove 104 is formed in an upper surface of the thrust plate 103 to form a thrust dynamic pressure bearing. The shaft 101 also has a dynamic pressure groove 105 in an outer peripheral surface, forming a radial dynamic pressure bearing. In the dynamic pressure bearing 100 thus constructed, a predetermined bearing fluid (lubrication oil) is filled in a gap 106 defined between the rotatably arranged shaft 101 and sleeve 102. The dynamic pressure grooves 104, 105 provided in the gap 106 serve to produce dynamic pressure in lubrication oil through their pumping actions. Thus, the shaft 101 is relatively rotatably supported by the sleeve 102 through dynamic pressure.
The actual use of the dynamic pressure bearing 100 of FIG. 4 require one to previously supply lubrication oil in the gap 106 between the shaft 101 and the sleeve 102. In a first lubrication method, the air within the gap 106 is sucked out into a vacuum or near vacuum state to introduce oil into the gap 106 by the action of atmospheric pressure. In a second lubrication method, a dispenser is used to drip lubrication oil to the gap 106 so that it can be introduced utilizing capillary action. In a third method, lubrication oil is previously applied to an inner periphery of the sleeve 102 or the like and then other bearing members are assembled in order.
The first method utilizing vacuum drawing requires a device such as a vacuum pump or vacuum chamber. Also, wiping the oiling hole is required after completing the vacuum lubrication. Meanwhile, in the second method using a dispenser, there are cases in which air bubbles are left in the gap 106. If air bubbles be introduced, there arises a concern that the air expands as temperature rises to thereby push out lubrication oil. Also, where the air bubbles enter in the gap, there is a concern of causing seizure or the like. Particularly, for a side closed structure such as the dynamic pressure bearing 100 closed at one end and opened at the other end, there are often cases where air bubbles may be left within the gap. In addition, the use of a dispenser takes time to fill lubrication oil, and is thus worse in terms of efficiency. In the third method of assembling parts after previously supply lubrication oil, there is a concern of air intrusion during the assembling process. There is also a concern that lubrication oil may leak out to an unnecessary portion of lubrication oil in nature.
The following means are provided in order to solve the problems encountered in the related art. That is, the following lubricating method is applied for a dynamic pressure bearing according to the present invention. First is a dynamic pressure bearing is assembled having a gap formed with a dynamic pressure groove and an open end and a closed end. Next, lubrication oil is dripped in a proper amount onto the open end of the dynamic pressure bearing. Finally, a centrifugal force is applied to the dynamic pressure bearing in a direction from the open end to the closed end to forcibly introduce the lubrication oil into the gap.
According to the invention, a centrifugal force is used to introduce lubrication oil into a gap of a dynamic pressure bearing, differently from the related art lubricating method using vacuum drawing or a dispenser. The use of a centrifugal force makes it possible to implement lubrication without intrusion of air bubbles in a dynamic pressure bearing of a side closed structure. Also, it is possible to reduce a time required for lubrication.